1. Field of the Invention
The present invention relates to an improved electromagnetic type reciprocating pump which is utilized for a compressor, vaccum pump and so on.
2. Description of the Related Art
A conventional electromagnetic type reciprocating pump comprises, as shown in FIG. 2, an electromagnet 100 having a coil 100a and core 100b and a piston 101 having a magnetic member 101a at one end portion. The coil 100a is connected to an AC power supply 103 via a rectifier (a diode) 102. The other end portion of the piston 101 is inserted into a cylinder 104 and urged by a coil spring 105 toward a cylinder head 104a. A suction valve 106 and exhaust valve 107 are provided at the cylinder head 104a.
In the aforementioned electromagnetic type reciprocating pump, the magnetization and demagnetization of the electromagnet 100 are repeatedly performed by a half wave-rectified pulse of alternating current. In the magnetization mode, the magnetic member 101a of the piston 101 is attracted, causing the piston 101 to move in a forward direction under a compression force to suck a fluid into the cylinder 104 via the suction valve 106. In the demagnetization mode, the piston 101 is moved, in a backward direction, under a reaction force of the coil spring 105, causing the fluid present within the cylinder 104 to be exhausted via the exhaust valve 107.
In the aforementioned electromagnetic type reciprocating pump, when the piston 101 is moved backward with the demagnetization of the electromagnet 100, the fluid i.e., gas, which is compressed within the cylinder 104 acts as a cushion. In a conventional fluid pump, when an input voltage to be applied to the electromagnet 100 is lowered, for some reason or other, at a time of starting for example, an amount of returning of the piston 101 becomes smaller due to a corresponding magnetic attraction force and an amount of fluid sucked becomes smaller, thus failing to obtain an adequate cushion action when the piston 101 is moved in a backward direction. As a result, the piston 101 hits against the cylinder head 104a to produce a pounding sound also known as piston shock. In a conventional general-purpose fluid pump, when the input voltage to be applied to the electromagnet is lowered so as to control a fluid pressure or amount, the aforementioned adverse situation is encountered. It is, therefore, necessary that a pressure regulator be mounted on the pump so as to regulate a cushion action.